1. Field of the Invention
The present invention relates to a design support system and a design method for circuit board of an electronic equipment which can transmit and receive electro-magnetic waves via an antenna, and to a noise analysis program.
2. Description of the Related Art
As multifunctional and high-speed electronic equipments, such as cellular phone, have been developed in recent years, unwanted radiation noises radiated from the electronic equipments may cause electro-magnetic interference (EMI) which can affect operations of other electronic equipments, hence, magnitude of the unwanted radiation noise is limited by law.
Electronic equipment manufacturers take EMI measures to estimate unwanted radiation noises externally radiated from electronic equipments prior to commercial production and to suppress generation of the unwanted radiation noises so as to obey regulatory values.
However, conventional measurement of unwanted radiation noises is far-field electro-magnetic measurement in which a measurement point is located far away from an electronic equipment. The primary purpose thereof is to inspect whether or not the unwanted radiation noises from the whole electronic equipment obey the regulatory values.
If unwanted radiation noises are estimated in order to take EMI measures after electronic parts and wiring of circuit boards constituting an electronic equipment have been fixed, arrangement of the electronic parts and the wiring must be totally redesigned, thereby resulting in a large amount of time and effort for taking EMI measures.
In a case where we can estimate electro-magnetic intensity in the vicinity of a circuit board constituting an electronic equipment, we can identify sources of unwanted radiation noises, thereby effectively taking EMI measures. The following patent document 1 discloses such a method for near-field electro-magnetic measurement.
The related prior art is listed as follows: Japanese Patent Unexamined Publication (koukai) JP-2000-206163, A.
The near-field electro-magnetic measurement has an advantage of identifying sources of unwanted radiation noises for effectively taking EMI measures. But the measurement is effective only in EMI affecting operation of another electronic equipment.
Meanwhile, in modern electronic equipments having communication function, such as cellular phone, actualized is a different type of noise problem in which a slight unwanted radiation noise generated from the particular electronic equipment may be picked up by a highly-sensitive antenna thereof, causing the electronic equipment to malfunction.
In general, for EMI measures, it is effective to shield chassis or circuit boards of electronic equipments. But a recent cellular phone has a part of a circuit board which can operate as an antenna. In this case, the above-described type of noise problem cannot be overcome by the conventional shielding.
Particularly, recent cellular phones are equipped with camera function and movie transmitting and receiving function, as well as the communication function. The above-described type of noise may adversely affect image characteristics as well as reception characteristics.
Thus, the conventional design support system and the conventional design method for circuit board take no account of such a problem as malfunction of an electronic equipment caused by interference of unwanted radiation noises generated from the particular electronic equipment into the circuit board via the antenna.